when u weight train it strains ur CNS, remeber ur brain is what controls ur muscles etc, the CNS is very important in strength training becuase it controls how much power and focus ur able to get out of ur muscle fibers
e.g rest breaks between sets of 5-7minutes for big compound lifts allow lots of time for the CNS to recover from the previous lift and give it time to have descent recovery to pull out ur next big lift
best example i can give is try to your deadlifts with 3 minute rest breaks, and then another workout do ur deadlifts with 5 minute rest breaks between sets
the strength difference and aggression in each set is dramatic becuase of the amount of time ur CNS has to recover
apart from rest breaks between sets theres also the rest needed between workouts,
this is why rest days are always reccomended becuase big workouts are stressing on ur CNS, hence why towards the end of a workout ur always fatigued or cant be fuked doing the last exercises, the last few reps ull never push hard becuase ur CNS is fatigueing
best example i can give is one week u might train legs one day, then train chest the next day
the following week u might train legs one day, and then 2 days later train chest
the strength difference for ur chest workouts will differ most likely, the second workout weeks chest workout most likely will be stronger due to the rest day uve incorporated, this is due to the CNS having time to recover from ur heavy leg workout
what im trying to address here is 2 workouts can be very stressing on ur CNS, especially if all day u said ur already doing strenous exercise, and if your interested in strength then u should be allowing alot of rest for ur workouts, big rest breaks between sets,
and if u wanna take it further, training 3-6 hours after waking is the prime time to train for strength becuase ur CNS is at its strongest point
im just sharing this info, what u choose ot do is your decison but consider these things before deciding whether 2 workouts a day is really a good idea, or maybe just you being to eager to train